The Scottish Naturalist. 3 1 7 



up with snow, to another where the seasons are comparatively 

 temperate, we cannot but believe that in course of time some 

 modification will take place in the form and habit of the species. 



The same species that in our hills reproduce themselves from 

 seed, in Greenland, north of Disco, have not time during their 

 short summer in which to ripen their seed, consequently seed- 

 lings are never met with ; and the extension of the range of any 

 given species would seem to be due to the creeping powers of 

 the individual which, with few exceptions, all possess, or to 

 plants being drifted downward on blocks of half-frozen mud and 

 ice containing plants and roots, torn out and hurried to the 

 shore. Circumstances have there compelled species to adapt 

 and accommodate themselves to their surroundings. 



Mr Wallace relates that many islands throughout the globe 

 now contains certain species both of animals and plants which 

 are peculiar to these islands, not being known to exist anywhere 

 else in the world. Many of these islands must at one time have 

 received their fauna and flora from the nearest continent by 

 former land -connection, and he accounts for the change of 

 species, which he contends must in many instances have taken 

 place, by such considerations as change or modification of 

 climate from continental to insular, which would produce a 

 series of changes, the most important of which would arise from 

 isolating small groups of individuals of many species, and thus 

 altering their relations to the rest of the organic world. Many 

 of these would be at once exterminated, while others, being re- 

 lieved from competition, might flourish and become modified 

 into new species. 



Any one at all acquainted with the genus Saxifraga, or that 

 of Primula, knows how difficult it is often to distinguish the 

 difference between species, sub-species, and varieties, the modi- 

 fications of form being seemingly endless. 



The American form of Azalea procumbens has a looser and 

 larger habit than our Scottish form, quite marked and distin- 

 guishable ; so also with the American form of Linncea borealis, 

 the leaves of which are much larger than our native form. 

 Again, there is a marked difference in Lychnis alfiiua, which in 

 Scotland is much dwarfer than the English or Continental form. 

 These variations of appearance are all permanent in cultivation, 

 and may not amount to what would constitute a difference in 

 species, only variety. 



What Mr Wallace contends for is, that provided always sufh- 



